SANITARY  ASPECTS  OF  MILK 


BY 


GAIL  MONROE  DACK 


THESIS 


FOR  THE 

DEGREE  OF  BACHELOR  OF  SCIENCE 


IN 


AGRICULTURE 


COLLEGE  OF  AGRICULTURE 

UNIVERSITY  OF  ILLINOIS 


1922 


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Digitized  by  the  Internet  Archive 
in  2016 


https://archive.org/details/sanitaryaspectsoOOdack 


TABLE  OF  COirrENTS 
Certific ate. 

Table  of  Contents. 

I Introduction. 

II  General  Milk  Contamination. 

III  Epidemiology  of  Milk. 

IV  Relation  of  Milk  to  Infant  Mortality. 

V Lactic  Acid  Bacteria. 

VI  Milk  Pasteurization. 


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SANITARY  ASPECTS  OF  MILK 


I.  Introduction 

Since  milk  ie  one  of  the  best  mediums  in  which  bacteria  may  grow  and 
develop,  the  sanitary  aspects  of  milk  are  of  prime  importance.  The  normal 
course  of  milk  generally  brings  many  different  types  of  organisms  in  con- 
tact with  it.  It  has  been  the  aim  of  the  writer  to  bring  together  data 
showing  the  sources  from  which  these  organisms  may  gain  entrance  into  the 
milk. 

Of  the  organisms  entering  milk  those  to  be  feared  are  the  pathogens. 
In  outbreaks  of  disease,  milk  is  one  of  the  first  sources  to  be  investi- 
gated. Too  great  stress  is  often  laid  on  milk  as  t?ie  spreader  of  disease. 
Some  of  the  various  diseases  spread  through  milk  will  be  discussed  and 
also  milk  in  relation  to  infant  mortality.  Pasteurization  has  been  found 
to  be  an  efficient  and  cheap  method  for  eliminating  disease  organisms 
found  in  milk. 


II.  General  Milk  Contamination. 


Udder. 

In  the  early  days  milk  was  thought  to  be  sterile  when  drawn  from  the 
udder  of  the  cow.  Russel  malces  the  following  statement: — "it 

has  been  proven  many  times  by  experiments  that  milk  from  healthy  animals 
when  secreted  in  the  milk  gland  in  the  udder  is  absolutely  germ  free.” 

It  is  a common  belief  now  that  milk  as  it  is  secreted  in  the  udder  of 
normal  healthy  cows  is  sterile.  Infection  may  readily  occur  in  the  udder. 
T^ard  ( examined  the  udders  of  nineteen  milch  cows  from  five  differ- 
ent dairies.  He  found  that  all  the  udders  harbored  bacteria  throughout 
their  whole  extent. 

The  udder  is  so  constructed  anatomically  that  bacteria  may  readily 

5 

enter  it.  Hastings  and  Hoffman‘S  (^907)  report  a bacteriological  examina- 
tion of  the  milk  from  the  various  quarters  of  an  animal  with  a leaking 
hind  quarter.  All  the  quarters  seemed  to  have  the  similar  bacterial 
count  and  the  count  of  the  leaking  quarter  was  no  larger  than  that  of  the 
other  quarters. 

The  numbers  of  bacteria  found  in  freshly  drawn  milk  seem  to  '^ary 
greatly.  Hastings  and  Hoffman  (^9'^7)  seem  to  think  that  1000  bacteria 
per  cubic  centimeter  is  not  exceeded  in  the  average  germ  count  as  drawn 
from  tne  udders  of  healthy  cows.  Harding  and  Wilson^  (191^)  i:i  en  exam- 
ination of  1250  samples  of  milk  direct  from  the  udders  of  seventy-eight 
cows  found  an  average  count  of  ^28  bacteria  per  cubic  centimeter.  They 
found  the  bacteria  to  be  about  three  times  as  nuiaerous  per  cubic  centi- 
meter in  the  back  quarters  as  in  the  front  quarters.  Also  that  the  age 


5 


of  the  cow  and  the  period  of  lactation  exerted  no  marked  influence  upon  the 
germ  content  of  the  udder.  The  fore  milk  was  found  to  contain  more  bacteria 
than  milk  taken  near  the  middle  of  the  milking.  Milk  drawn  toward  the  end 
of  the  period  was  found  to  contain  relatively  few  bacteria. 

Bacteria  may  gain  entrance  to  the  milk  from  two  sources.  From  the 
ducts  of  the  teat  they  may  easily  enter.  They  may  also  gain  entrance  from 
the  udder.  Probably  many  forms  that  enter  the  udder  find  an  environment 
unsuitable  for  their  existence  and  are  probably  killed  oat.  This  would 
tend  to  exe^'t  a selective  action  upon  the  types  of  organisms  i^ich  may  thrive 
there.  Hastings  and  Hoffman^  found  an  organism  which  they  described 

as  a Streptococcus  similar  to  Strept  pyogenes  in  morphology  and  biochemical 
relations.  They  found  that  ninety  percent  of  the  udder  bacteria  were  com- 
prised of  this  organism.  In  tuberculous  udders  the  tuberculosis  germ  gets 
into  the  milk.  Coiin^  (I9I0)  states  that  cocci  forms  come  mostly  from  the 
milk  ducts.  Harding  and  Conn^  (19^5)  found  the  udder  flora  to  be  charac- 
terized by  a lack  of  motility,  of  spore  formation  and  of  gas  formation. 

They  found  them  to  be  composed  of  gram  positive  organisms  and  mostly  of 
micrococci. 

Evans^  ( 19^'^)  divided  the  udder  bacteria  into  three  groups;  strepto- 
cocci, micrococci,  and  bacilli.  She  differentiated  between  the  long  chain 
streptococci,  which  may  be  of  a vljulent  type  and  the  saprophytic  Str. 
lacticus  (Kruse).  She  was  able  to  isolate  Str.  lacticus  only  once  out  of 
192  samples  studied.  She  concluded  from  this  that  Str.  lacticus  does  not 
localize  and  mviltiply  in  the  udder.  She  found  micrococci  to  occur  most 
frequently  in  the  udder,  isolating  them  from  11^  out  of  I92  samples.  The 
majority  of  staphylococci  of  the  udder  she  found  to  be  nonvlrulent.  She 


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isolated  s bacilli  related  to  3.  abortus.  Moore^  (.^9^^)  states  that  the 
species  vary  according  to  the  care  and  environ-^ent  of  the  cow. 

In  normal  cows  of  good  health  the  udder  bacterial  flora  seems  to  be 

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of  little  significance.  In  cases  of  disease  this  would  not  hold.  Colwell 
(I9I7)  bas  shown  that  cows  infected  with  mamraitis  produce  milk  with  a very 
high  bacterial  count.  He  found  that  in  every  instance  where  by  physical 
examination  one  quarter  was  known  to  be  infected,  one  or  more  of  the  appar- 
ently healthy  quarters  proved  to  be  infected  with  similar  organisms.  This 
shows  that  even  though  milk  from  the  infected  quarter  be  discarded,  the 
other  quarters  v/ould  raise  the  bacterial  count  of  milk.  In  practically 
all  of  the  investigations  made,  very  few  instances  have  been  reported  where 
organisms  of  high  virulence  or  pathogenic  have  been  isolated  from  milk 
aseptic  ally  taken  fromthe  udders  of  healthy  animals. 

Utensils. 

It  has  been  known  for  a long  time  that  utensils  played  a large  part  in 
contaminating  milk  ■with  bacteria.  Utensils  v/hich  are  not  thoroughlv  w'ashed 
and  grained  form  excellent  quarters  in  w^hich  bacteria  may  develop. 

9 

Stocking,  Jr.'  in  I9O7  ma.de  some  studies  on  the  various  types  of  milk 
pails  used.  He  found  the  covered  pail  to  be  of  a distinct  advantage  in 
excluding  dirt  end  bacteria  from  milk.  He  found  that  the  form  of  cover  made 
little  difference,  provided  it  was  a device  practical  for  use  and  the  ares 
through  which  dirt  could  gain  entrance  to  milk  was  reduced  ns  much  as  possible. 
In  regard  to  the  different  strainers,  the  desirability  of  a straining  devise 
depends  upon  the  style  used.  The  use  of  a.  strainer  in  a pail  whe’-e  the  dirt 
which  fells  into  the  opening  is  llkelj'^-to  be  driven  through  by  succeeding 
streams  of  milk  was  found  to  be  very  undesirable  and  to  in  lure  the  keeping 


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quality  of  the  milk,  ^beorbent  cotton  as  a strainer  v/as  found  to  be  a decid- 
ed advantage  in  preventing  the  entrance  of  bacteria  into  the  milk. 

Prucha  end  others  (I9IS)  studied  the  germ  content  of  milk  as  influenced 
by  utensils.  They  found  the  utensils  rather  then  the  barn  conditions  to  be 
the  principal  sources  of  bacteria  in  milk.  Then  all  the  utensils  commonly 
used  in  handling  milk  were  thoroughly  strained,  the  bottled  milk  had  uni- 
formily  only  about  bacteria  per  cubic  centimeter  but  as  soon  as  strain- 

ing was  omitted  the  bottled  milk  frequently  contained  several  hundred  thou- 
sand bacteria  per  cubic  centimeter.  They  found  the  greatest  contamination 
to  come  from  the  most  complex  apnaratus  such  as  the  clarifier  and  the  bot- 
tle filler.  They  compared  the  following  relative  proportions  of  bacterial 
contamination  from  various  utensils  with  the  barn  influences: — pails  add 
about  eleven  times  as  many  bacteria  to  milk  as  the  barn  influences;  the 
strainer  one  and  one-half  times  as  many;  the  clarifier  thirty  times  as  many; 
the  cooler  ten  times  as  many;  and  the  bottle  filler  sixty  times  as  many;  mak- 
ing a total  of  112  times  as  manv  added  by  the  utensils  as  by  the  barn  factors. 

From  what  has  been  given  it  can  be  seen  that  the  need  for  careful  hand- 
ling of  milk  cannot  be  too  strongly  stressed.  In  selecting  dairy  utensils 
it  should  be  kept  in  mind  that  they  are  one  of  the  chief  sources  of  contam- 
ination and  only  that  apparatus  which  can  best  be  cl  aned  and  sterilized 
should  be  selected.  One  needs  but  only  to  visit  some  of  the  dairy  farms 
to  see  how  careless  and  thoughtless  many  fanners  are  in  the  care  of  the  milk 
pails  and  cane.  Much  of  this  is  due  to  ignorance  on  the  part  of  the  farmer 
but  with  proper  instmction  such  as  may  be  obtained  from  fann  journal  a and 
papers,  this  condition  ought  to  be  imnroved. 


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Low  Temperr.tures. 

Ravenel  and  others  (19^0)  studied  the  bacterial  flora  of  milk  held 
at  low  temperatures.  They  found  that  in  milks  held  at  plus  nine  degrees 
centigrade  there  was  a clumping  of  the  casein  and  fat,  no  increase  in  the 
bacteria  developing  on  agar  and  gelatin,  and  an  increase  in  the  amount  of 
soluble  nitrogen  and  a decrease  in  the  acidity.  They  found  a marked  in- 
crease in  the  bacterial  content  of  milks  held  at  zero  degrees  centigrade 
v^ich  resulted  in  an  increase  in  acidity  and  an  increase  in  the  percentage 
of  soluble  nitbogen  so  that  it  eventually  amounted  to  over  seventy  percent 
of  the  total  nitrogen  and  a decrease  in  the  total  nitrogen  content  due  to 
the  liberation  of  free  nitrogen.  They  found  putrefactive  organisms  to  grow 
well  at  low  temperatures.  There  is  danger  of  cream  being  held  too  long  at 
low  temperatures.  This  is  due  to  the  demand.  They  state  that  cream  held 
for  a long  time  at  low  temperatures  may  be  normal  in  appearance  end  taste 
but  it  may  contain  the  by-products  of  the  putrefactive  bacteria  in  such 
amounts  as  to  render  it  harmful.  Ice  cream  poisoning  which  is  quite  common 
was  found  to  be  due  to  bacterial  by-products, 

Ravenel  and  others  (19^9)  made  the  following  statement  with  regard 
to  milk  held  at  low  temperatures: — "In  practical  effects  cold  storage  is 
identical  with  pasteurization  since  it  removes  from  the  sphere  of  action 
that  class  of  bacteria  that  prevent  the  growth  of  harmful  bacteria  to  de- 
velop." They  found  that  some  organisms  disappear  during  holding  while 
others  become  acclimated  to  lowrer  temperature  of  incubation.  Micrococcus 
aurantiacus  (Cohn)  and  micrococcus  ovalis  (Esoherich)  v^ich  belong  to  the 

acid  forming  group  was  found  to  be  most  predominant. 

12 

Pennington  and  others  found  that  in  milk  a cream  held  at  a temper- 
ature of  zero  degrees  centigrade,  proteolysis  of  the  casein  was  primarily 


7 


of  bocterial  origin.  They  state  that  the  proteolysis  of  lactalburain  is 
due  primarily  to  native  enzjrmes  in  milk.  They  found  that  the  bacterial 
flora  and  native  milk  enzymes  by  their  combined  action  produced  more  rapid 
proteolytic  changes  tharx  were  produced  by  either  agent  alone.  Also  that 
the  general  trend  of  proteolysis  by  the  different  means  mentioned  in- 
volved a breaking  down  of  true  proteins  and  their  passage  through  caseose 
and  peptone  to  amino  acids.  The  fermentation  of  lactose  with  the  formation 
of  lactic  acid  was  claimed  to  be  due  largely  if  not  entirely  to  bacterial 
action. 

The  above  changes  (digestion  of  protein,  fermentation  of  lactose  and 
increased  acidity)  were  found  to  be  progressive  changes  and  accompanied  by 
lowering  the  point.  The  I. number  and  index  of  refraction  of  butter  fat 
remained  unchanged. 

From  the  foregoing  it  may  be  clearly  seen  that  milk  kept  at  a low 
temperature  for  a long  time  will  contain  a very  large  bacterial  flora. 

This  flora  consisting  largely  of  putrefactive  types  of  microorganisms 
will  render  the  milk  unsafe  for  drinking  purposes.  Many  of  the  decompo- 
sition products  are  very  poisonous  and  toxic,  though  they  may  not  always 
be  detected  by  tast  and  odor.  Little  has  been  done  in  regard  to  studying 
the  bacterial  toxin  formed  at  these  temperatures. 

Barn  Factors. 

Prucha  and  T7eeter^^  (^9^7)  studied  the  barn  factors  as  influencing 
the  germ  content  of  milk.  The  study  was  conducted  in  three  dairy  barns 
differing  widely  in  the  degree  of  cleanliness.  Samples  were  taken  from 
the  milk  of  individual  cows  as  the  milk  was  brought  from  the  barn  to  the 
milk  room.  The  germ  content  of  each  sample  was  determined.  The  germ 


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content  of  individual  eainpleB  was  found  to  vary  from  three  to  218,250  bac- 
teria per  cubic  centimeter.  They  found  that  the  sanitary  conditions  of  the 
barns  did  not  effect  the  germ  counts  appreciably.  They  conclude  that  even 
under  wide  extremes  in  barn  conditions  it  is  possible  to  produce  milk  with 
a germ  content  of  less  than  10,000  bacteria  per  cubic  centimeter  when  the 
utensils  are  properly  prepared. 

Other  Factors. 

14 

Stocking  Jr,  (IpOb)  observed  that  feeding  hay  or  dry  grain  before 
or  at  milking  time  fills  the  atmosphere  of  the  stable  with  dust.  The 
dust  settled  in  the  milk  pails  carrying  with  it  bacteria  and  hence 
increasing  the  bacterial  count  in  the  milk.  He  found  the  effect  of  feeding 
dry  corn  stover  before  or  at  milking  time  to  have  a similar  but  more 
marked  effect. than  when  hay  was  fed.  This  is  due  to  the  fact  that  more 
dust  was  given  off  from  the  dry  corn  stover. 

The  practice  of  wiping  the  flank  and  udder  of  the  cow  with  a damp 
cloth  before  milking  was  found  to  be  beneficial  as  it  reduced  the  number 
of  bacteria  falling  into  the  milk.  Brushing  the  cows  at  milking  time  was 
found  to  be  undesirable  as  the  hair  and  dust  set  free  settled  in  the  milk 
pail  and  increased  the  germ  content.  Harding  and  others  ^^(1915)  found 
that  when  cows  were  cleaned  with  a brush  and  comb  at  the  rate  of  two  cows 
per  minute  was  practically  the  same  as  vhen  the  same  cows  were  treated 
with  a vacuum  cleaner  at  the  rate  of  one  cow  per  minute. 

Stocking  Jr.  observed  that  stripping  a cow  dry  tended  to  reduce 
the  number  of  bacteria  found  in  the  milk  at  the  next  milking.  He  found 
that  a slightly  lower  germ  content  was  found  in  the  milk  at  the  time  of 
the  next  milking.  He  found  that  a slightly  lower  germ  content  was  obtained 


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where  the  foremilk  was  discarded.  The  difference  however  proved  to  be 
very  small. 

Harding  and  others  found  that  clipping  the  udder,  flank  and 

adjoining  portions  of  the  cow  slightly  increased  the  germ  content  of  the 
milk  v^en  the  cow  was  cleaned  either  with  a vacuum  cleaning  machine  or  by 
hand. 


Plies  are  a big  factor  in  the  spreading  of  germs  to  milk.  They 
carry  large  numbers  of  all  kinds  of  bacteria.  They  ere  agents  in 'the 
distribution  of  intestinal  diseases.  This  danger  can  be  greatly  reduced 
by  the  care  of  the  utensils.  Also  the  sanitary  conditions  observed  are  of 
great  significance. 

Lastly  and  one  of  the  most  important  elements  which  contribute 
bacteria  to  milk  is  the  milker.  Uxxch  of  this  is  due  to  lack  of  intelligence 
on  his  part.  The  personal  habits  of  the  milker  is  another  big  factor.  Many 
diseases  have  been  spread  through  milk  w^iere  milk  was  originally  contaminated 
by  the  milker.  The  so  called  process  of  "wet  milking"  where  the  milker 
dampens  the  teats  with  milk  while  milking  is  an  example  of  a man  with 
poor  personal  habits,  yet  this  sort  of  milking  is  quite  widely  resorted 
to  in  many  of  the  dairies. 

Much  has  been  said  about  milk  contamination;  Now  the  question  arises;- 
how  may  this  condition  be  improved?  A few  years  ago  the  score  card  came  out 
whereby  dairies  could  be  scored  in  regard  to  the  points  which  were  consid- 
ered’of  importance  in  milk  contamination.  This  had  a far  reaching  effect 
and  proved  to  be  very  useful  in  educating  the  farmers  along  the  lines  of 
milk  contamination. 

North^^  is  of  the  opinion  that  the  score  card  failed  to  emohasize 


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the  factors  of  primary  importnnce.  He  cites  a case  v^iere  an  improvement 
was  made  in  another  way.  Bacteriologists  were  sent  to  a shipping  station 
at  Sparks,  ^d.  They  gave  advice  to  the  farmers  and  cooperated  with  them 
in  helping  to  lower  the  bacterial  count.  As  a result  of  their  efforts  in 
6 weeks  the  bacterial  count  was  reduced  from  over  2,000,000  to  under 
^0,000  bacteria  per  c.c. 

The  above  method  proved  to  be  quite  successful  but  to  give  it  general 
application  would  be  a matter  of  considerable  time  and  expense.  One  of  the 
biggest  difficulties  which  bacteriologists  have  to  face  is  the  clumsiness 
of  the  methods  in  making  a bacterial  count.  The  direct  count  method 
involves  a great  deal  of  care  and  technique  and  at  the  best  the  results 
are  only  tentative.  If  it  is  carried  on  very  extensively  it  proves  to 
be  a great  strain  on  the  eyes  of  the  observer.  The  plate  count  method 
requires  more  technique  and  time  and  also  a* great  deal  more  apparatus. 


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11 

Bibliography. 

1 Russel,  H.L. ; The  Sources  of  Bacterial  Infection  and  the  Relation  of  the 

Same  to  the  Keeping  Quality  of  Milk.  Univ.  Tis.  Agr, 

Exp.  Sta.  11th  Ann.  Rpt.j  1^0  (189^). 

2 Ward,  A.R.j  The  Invasion  of  the  Udder  by  Bacteria.  Cornell  Univ.  Agr. 

Exp.  Sta.  Bui.  178  (IPOO). 

5  Hastings,  E.G.  end  Hoffmann,C.;  Bacterial  Content  of  Milk  of  Individual 

Animals.  Wis.  Agr.  Exp.  Sta.  Research  Bui. 6 pp.  1£9- ^907) 

4 Harding,  H.A.  and  Wilson,  J.K.j  A Study  of  the  Udder  Flora  of  Cows. 

Tech.  Bui.  No.  27  N.Y.  Agr.  Exp.  Sta.  (March  19^5) • 

5 Conn,  H.W. j Practical  Dairy  Bacteriology.  Orange  Judd  Co.(l9l0)  pp.59* 

6 Evans,  Alice  C.;  Bacteria  of  Milk  Freshly  Drawn  from  Normal  Udder. 

Jour.  Inf.  Diseases  18:457> ( 19 • 

7 Moore,  V.A.;  The  Normal  Bacterial  Invasion  5f  Cow’s  Udder.  Principles 

of  Microbiology.  Macmillan  Co.  (19^^) 

8 Colwell,  R.C . ; Inf luence  of  Gargety  and  High  Count  Cows  on  the  Number  of 

Bacteria  in  Milk.  Abst.  Bact.  1:^8  (19^7). 

9 Stocking  Jr.  W.A.j  Comparative  Studies  with  Covered  Milk  Pails.  Storrs 

Agr.  Exp.  Sta.  Bui.  No.'^8(May  1907). 

10  Prucha,M. J. jWeeter,H.M.  and  Chambers, W.H.  Germ  Content  of  Milk  (As 

Influenced  by  Utensils)  U.  of  111. Agr.  Exp.  Sta.  Bui.  No. 

204  Feb.  ( I9I6). 

11  Ravenel,  M.P.;  Hastings,  E.G.  and  Hammer,  B.W. j The  Bacterial  Flora  of 

Milk  Held  at  Low  Temperatures.  Journ.  Inf.  Diseases.  Vol.7s 

(I9I0). 

12  Penington,M.E;  Hepburn,  J.S. ; St . John, E.Q. ;Witmer, E;  Stafford,  M.0.;and 

Burrel,J.I.  Journal  of  Bio-Chem.  .Bacterial 

and  Enzymatic  Changes  in  Milk  and  Cream  at  O^C. 

15  Prucha,  M.J.  and  Weeter,  K.M, ; Germ  Coritent  • of  "Milk  (As 'Influenced  by 

Factors  at  the  Barn).  U.  of  111.  Agr.  Exp.  Sta.  Bui.  No. 1p9 
May  (1917). 

14  stocking,  Jr.,  W.  A.j  Quality  of  Milk  Affected  by  Coromon  Doirj'’  Practices. 

Storrs  Agr.  Exp.  Sta.  Bui.  No.  42.,  June,  I9O6. 

15  Harding,  H.  A.;  The  Effect  of  Certain  Dairy  Operations  Upon  the  Germ 

Content  of  Milk.  (H.  A.  Harding,  G.  L.  Ruehle,  J.  K. 

Wilson,  and  G.  A.  Smith)  N.  Y.  Agr.  Exp.  Sta.  Bui. 

565:197>  I9I5. 


w ym^^i 


mmm 


BKf  r-y  ,.  >x[  , sr**' 


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v^V 


■„;  .-i  .,  < 


WJK.  1 ’’  ' y I > • I.  ' ^ V T • ' , .'  ' ^ ^ .'.  »'  .VA-,  i.  • * ' • 

',  . • '^'Jv  •aiii^i  ,i4»‘(-»*^>?tF 'o'^f  \iilTO  .Vj{ 

.W  -■  A-Ar‘>  :■  ' 

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•“■  ■ ■/  y ■- ^>^*' "' • .r,>r 

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16  North,  Charles  E.j  The  Dairyman  Versus  the  Dairy.  Am.  Joum.  Pub. 

Health,  50 19-525  19 15- 

17  Bergey,  D.  H.;  M.  D.;  An  Investigation  on  the  Value  of  Certain  Sanitary 

and  other  Precautionary  Measures  Upon  the  Bacterial 
Content  of  Milk.  Penn.  Dept,  of  Agr.  Pep,  Part  I, 

p.  155- 165  1900. 

18  Esten,  M. , and  Mason,  C.  J. ; Sources  of  Bacteria  in  Milk.  Storrs 

Agr.  Exp.  Sta.  Bui.  No.  5I  65-IO7  1907-19^9 


15 


III  Epideraiology  of 

Milk  being  an  excellent  medium  for  bacterial  g’"owth  has  been  one 
of  the  first  sources  to  be  investigated  in  epidemics  of  various  kinds, 

Sorae  of  the  diseases  of  human  origin  carried  through  milk  as  a medium 
are — diptheria,  Asiatic  cholera,  diarrhea, ( shiga  and  flexner)  typhoid 
and  paratyphoid  fever,  scarlet  fever,  tuberculosis,  septic  sore  throats 
and  others. 

Many  of  the  pathogenic  organisms  gain  entrance  into  the  milk  f lo  m the 
milker  or  utensils.  Many  such  cases  have  been  observed  especially  with 
Typhoid.  A typhoid  "carrier"  can  very  easily  contaminate  a wiiole  milk 
suppler.  Such  cases  have  been  amply  demonstrated  from  time  to  time. 

Diptheria. 

Diptheria  is  a disease  caused  by  B.  Diptheria.  It  is  spread  chiefly 
through  secretions  from  the  mouth  and  nose.  It  could  readily  be'  spread 
by  the  handling  of  milk  by  one  who  is  affected  with  it.  In  an  investiga- 
tion carried  on  in  Massachusetts  by  Kelly^  (191^)*  diptheria  transmission 
through  raw  milk  was  found  to  be  of  so  rare  occurrence  that  it  was  con- 
sidered negligible. 

In  a study  of  twenty-eight  instances  diptheria  existed  at  the  farm 
or  dairy  arid  in  ten  instances  the  disease  was  attributed  directly  to  the 
cows  having  garget,  chapoed  and  ulcerative  affections  of  the  teats  and 
udder. 

Asiatic-  Cholera, 

The  organism  Sp.  cholerae  was  found  to  be  the  cause  of  Asiatic  cholera. 
The  organism  is  discharged  in  the  feces  of  the  sick  and  of  the  carriers. 

From  this  source  it  can  be  readily  spread  by  flies,  by  carelessness  on  the 


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part  of  the  one  affected  and  in  innumerable  other  ways.  The  vibrio  requires 
a neutral  or  slightly  alkaline  mediuim  for  growth  and  perhaps  for  this 
reason  milk  does  not  serve  as  a very  effective  carrier.  Milk  apparently  is  not 
a very  important  agent  in  spreading  this  disease. 

Typhoid  Fearer. 

Typhoid  fever  is  one  of  our  common  diseases.  The  typhoid  germ  is 
discharged  in  the  feces  and  from  this  source  it  can  readily  be  spread.  In 
outbreaks  of  typhoid  fever  often  the  milk  is  blamed  and  unduly  so.  Kelly ^ 

( I9I0)  in  a statistical  study  of  milk-borne  infections  finds  that  only 
5 per  cent  of  the  total  cases  of  typhoid  reported  can  be  attributed  to 
milk.  This  figure  does  not  check  popular  statements  which  place  it  at  a 
much  higher  lesrel. 

p 

Busey  and  Kober  ( 19^9)  in  n study  of  1^6  epidemics  traceable  to  a 
specific  pollution  of  the  milk  find  that  in  I09  instances  there  is 
evidence  having  prevailed  on  the  farm  or  dairy.  In  5^  epidemics  the  germs 
reached  the  milk  by  soakage  into  well  water  with  which  the  utensils  were 
washed.  In  instances  milk  dilution  with  polluted  water  was  admitted. 

Scarlet  Fever. 

Many  attempts  have  been  made  to  locate  the  causal  organism  for 
scarlet  fever.  As  yet  the  causal  organism  has  not  been  definitely  proved. 

The  trs-nsmission  of  scarlet  fever  through  milk  as  a mediam  has  been  found 
to  assume  little  importance.  The  per  centage  of  cases  that  can  be  traced 
to  milk  has  been  found  to  be  very  small.  As  constrasted  to  diptheria  the 
percentage  ofscsrlet  fever  cases  traceable  to  milk  is  the  larger. 

p 

Busey  and  Kober  (I9O9)  in  a study  of  7^-  epidemics  spread  through  the 
medium  of  milk  find  that  in  instances  that  the  disease  prevailed  either 


15 


at  the  farm  or  dairy.  In  6 inatancea  persona  connected  with  the  dairy 
either  lodged  in  or  visited  infected  houses. 

Tuberculosis. 

Tuberculosis  is  one  of  the  common  and  worst  menances  with  which 
sanitarians  have  to  deal.  A vast  amount  of  money  and  time  hss  been  expended 

m 

in  investigating  this  phase  of  the  subject.  Milk  has  long  been  known  to  be 
one  of  the  chief  carriers  of  tuberculosis.  Adults  possess  a great  deal  more 
resistance  to  bovine  tuberculosis  than  do  children. 

Anderson^{ I909)  in  an  investigation  of  225  samples  of  milk  found  that 
15  of  them  or  6,72  percent  contained  sufficient  tuberculosis  organisms', to 
cause  the  typical  tuberculosis  symptoms  in  the  animals  inoculated.  11  percent 
of  the  dairies  which  he  examined  contained  tuberculosis  virulent  for 
guinea  pigs. 

Practically  none  of  the  pulmonary  tuberculosis  is  due  to  bovine 
bacteria.  Tuberculosis  seems  to  run  in  rather  definite  stages.  The  pro- 
dromal stage  being  the  stage  in  which  incubation  occurs.  This  stage  is 
followed  by  a period  of  sickness.  Prom  this  stage  either  death  will  occur 
or  there  will  be  a period  of  recovery. 

Long^^(l92l)  reports  a very  interesting  case.  Robert  Goben  of  Edgar 
County,  Illinois  had  his  cattle  tested  for  tuberculosis  end  one  of  the 
covfs  reacted  to  the  tuberculin  test.  He  did  not  believe  in  the  tuberculin 
test  and  later  took  the  condemned  tag  out  of  the  animals  ear.  The  cow  looked 
healthy  and  he  told  his  men  there  was  nothing  the  matter  with  her.  He 
talked  so  much  that  one  of  his  tenants  Jas.  Kelly  was  induced  to  take  her 
in  payment  for  work  he  had  done  for  Goben.  Kelly  used  her  for  a family  cow. 

In  Kelly’s  family  there  were  seven  children.  In  the  spring  some  of  the 


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children  commenced  to  complain  and  were  sickly.  A Doctor  was  consulted 
and  five  of  the  children  were  found  to  have  tuberculosis.  Tlie  youngi^st 
child  was  still  nursing  and  the  older  child  was  not  allowed  to  have  any 
of  the  milk  as  it  vms  thought  better  to  give  it  to  the  younger  children. 
The  five  children  affected  were  sent  to  a tuberculosis  ©anitarium  v&iere 
they  will  be  properly  cared  for.  It  is  thought  that  one  of  the  children 
will  die.  Goben  was  fined  one  hundred  and  fifty  dollars  for  selling 
a tuberculous  animal.  The  cow  when  killed  and  posted  shov/ed  generalized 
tuberculosis. 

Great  effort  has  been  made  in  the  past  few  years  to  clean  up  the 
tuberculosis  scourge.  The  discovery  of  tuberculin  has  played  a large 
part  in  making  this  possible.  Tuberculin  was  discovered  by  Koch  in 
I89O.  It  is  a glycerinated  broth  culture  of  tuberculosis  organisms  where 
the  organisms  have  been  killed  and  filtered  off.  This  may  be  given  in 
various  ways.  Ninety-eight  percent  of  the  positive  reactors  to  this  test 
show  lesions  on  autopsying  while  eighty-five  percent  of  the  non-reactors 
show  no  lesions.  If  this  test  were  made  compulsory  a greater  advancement 
toward  cleaning  up  tuberculosis  could  be  made. 

Septic  Sore  Throat. 

Septic  sore  throat  is  caused  by  the  Smith  streptococcus.  Milk  afford 
an  excellent  mediam  in  which  it  may  develop.  The  disease  is  character- 
ized by  a sudden  onset,  high  and  irregular  fever,  inflammation  of  the 
fauces,  marked  enlargement  of  the  cervical  glands,  particularly  in  the 
case  of  children.  The  course  is  much  longer  and  the  symptoms  more  severe 
than  in  tonsillitis.  The  joints  are  often  affected  and  often  the  heart 
and  kidneys  are  seriously  damaged;  middle  ear  disease  and  erysipelas 


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sonietimeB  result,  pneumonis  nnd  peritonitis  ’nay  develop  and  terminate 

CZ 

fatally.  The  above  symptoms  have  been  described  by  Parker'^(  17)  • 

Septic  sore  throat  seems  fortunately,  to  be  relatively  rare.  It 
nearly  always  occurs  in  epidemic  form  and  is  of  more  serious  consequences. 

Streptococci . 

Streptococci  seem  to  thrive  very  well  in  milk.  Various  types  of 
streptococci  are  found  to  be  present  in  apparently  normal  udders.  The  big 
difficulty  arises  when  we  try  to  separate  the  pathogenic  from  the  non 
pathogenic  or  harmless  types.  ’.louth  cultures  from  cows  were  found  to 
ferment  dextrose,  saccharose,  lactose,  mannite  and  frequently  raffinose,  but 
were  almost  without  effect  on  starch  or  glycerine.  Udder  cultures  were 
characterized  by  general  lack  of  f ermentati<ve  ability,  which  was  limited 
almost  entirely  to  dextrose,  saccharose  end  lactose,  with  a comparatively 
small  namber  utilizing  mannite,  glycerine  and  gelatin. 

Leucocytes  have  been  found  to  be  most  numerous  in  cases  of  disease. 

Many  leucocytes  and  streptococci  are  in  the  normal  milk  of  the  healthy 
cow.  A high  leucocyte  count  (over  60  polynuclear  leucocytes  to  a 1/12 
oil  immersion  field)  should  be  looked  into.  Garget  or  other  infection 
off  the  udder  might  be  present. 

A streptococcus  virulent  for  animals  but  which  differs  from  streptococcas 
pyogenes  in  more  abundant  growth,  in  being  encapsulated  and  not  forming 
dhains, ,and  causing  but  little  hemolysis  occur  in  predominating  numbers 
in  epidemic  sore  throat  of  milk  borne  origin.  On  artificial  cultivation 
the  strains  sooner  or  later  assume  the  characteristics  of  streptococcus 
pyogenes.  Cultures  on  blood  agar  plates  from  ordinary  milk  usually  gives 
rise  to  colonies  of  streptococci  that  do  hot  cause  any  hemolysis  but  the 


18 


injection  of  rabbits  with  milk  "slime"  practically  always  causes  infection 
with  encapsulated,  but  otherwise  typical  hemolytic  streptococci.  This 
demonstrates  that  the  blood  agar  plate  method  is  not  reliable  in  searching 
for  streptococcus  pyogenes  in  milk. 

If  streptococcus  pyogenes  is  placed  in  unheated  milk  it  becomes 
modified  so  as  to  correspond  to  the  streptococcus  in  epidemic  sore  throat. 

Hemolytic  streptococci  have  been  found  to  be  killed  by  the  acidity 
of  sour  milk  in  5 hours.  The  growth  of  hemolytic  streptococci  in  normal 
milk  is  inhibited  by  the  growth  of  other  bacteria. 

The  mastitis  causing  a high  bacterial  count  has  almost  without 
exception  been  due  to  streptococci.  Cows  have  been  found  to  be  "carriers" 
and  infection  has  been  found  to  be  carried  as  long  as  5 years  by  a single 
cow.  Milking  machines  have  been  found  to  be  simple  carriers  of  streptococci. 

Neither  the  fecal  nor  the  skin  streptococci  have  been  isolated  from 
the  bottled  milk  with  any  great  frequency.  These  types  are  non-hemolytic . 

The  skin  streptococci  have  been  found  to  produce  acid  in  dextrose,  lactose, 
saccharose,  maltose,  raffinose,  raannite  and  salicin  but  fail  to  acidulate 
media  containing  inulin.  The  fecal  streptococci  are  characterized  by 
the  formation  of  large  amounts  of  acid  in  dextrose,  lactose,  saccharose, 
maltoBej  raffinose,  inulin  and  salicin. 


I 


I 


' • • i 


19 


Bibliography. 

1 Kelly,  Eugene  R.  M.D;  Milk-Borne  Infection  in  the  Transmission  of 

Huiaan  Communicable  Diseasess  The  Quantitative  Relationship oof- 
American  Med.  Assoc.  Journal  67  port  2 ppl997~l999  (I9l'^)* 

2 Busey  and  Kober;  Epidemiology  of  Milk.  Treasury  Dept.  Hygeinic  Lab.  Bui. 

No.  5^  Gov'n  Printing  Office  page  ^9  (19^9) 

3 Anderson,  John;  The  Frequency  of  Tubercle  Bacilli  in  the  Market  Milk 
of  the  City  of  Fash.,D.C.  Milk  and  Its  Relation  to  Public 
Health  Bui.  No.  Hygeinic  Lab.  Treasury  Dept.  Gov'n 
Printing  Office.  (I9O9) 

Illinois  is  Cleaning  Up  on  Tuberculosis.  Holstein  Friesian 
World  Vol.  XVIII  No.  57-  page  560^ 

Bacteria  in  Milk.  City  Milk  Supply  1st  Ed.  t^^Graw-Hill 
Book  Co.  (1917). 

Some  Practical  Considerations  on  the  Presence  of  Leucocytes 
and  Streptococci  in  Milk.  Am.  Jour.  Pub.  Health  2:962. 

The  Significance  of  Leucocytes  and  Streptococci  in  Milk. 

Milk  and  Its  Relation  to  Public  Health.  Bui.  No.  56. 

Hygienic  Lab.  Treas-iry  Dept.  Gov’n  Printing  Office,  p.  9l* 

1909. 

Rogers,  L.  A.;  and  Dahlberg,  A.  0.;  The  Origin  and  Some  of  the  Streptococci 
found  in  milk.  Journ.  Agr.  Res.  ItApl. 

Rosenow,  E.  C.;  A Study  of  Streptococci  from  Milk  and  from  Epidemic  Sore 
Throat,  and  the  Effect  of  Milk  on  Streptococci.  Journal 
of  Inf.  Disease,  page  ^^5-5^6  I9I2. 

Davis,  D.  J.;  The  Growth  and  Viability  of  Streptococci  of  Bovine  and 

and  Human  Origin  in  Milk  and  Milk  Products.  Journ.  Inf. 

Die.  15:?78-568.  l9l^^. 

Moak,  H.,  M,  D.;  Control  and  Eradication  of  Infectious  ?v1astitis  in  Dairy 
Herds.  Cornell  Veterinarian.  April,  I9I6. 

Jones,  F.  S.,  V.  M.  D. ; The  Source  and  Significance  of  Streptococci  in 
Market  Milk.  Journal  of  Exp.  Med.  ^1  s 1 • I92O. 


4 Long,  C.M.; 

5 Parker,  H.N.; 
Scannel,  J.J.; 
Miller,  Wm.  W. ; 


•»  V :i  r-.  • fl 


J il  111  it  • 


20 


IV.  Relation  of  Milk  to  Infant  Mortality. 

A vast  ajnount  of  work  has  been  done  to  lessen  the  death  rate  of  infants. 
The  New  York  Milk  Committee^  carried  on  work  through  milk  stations  in  ten 
of  the  largest  cities  in  the  United  States.  The  work  was  carried  on  in 

As  a result  of  their  work  which  included  the  histories  of  babies, 

they  found  a marked  reduction  in  infant  mortality  during  that  year.  The 
stations  established,  issued  advice  to  mothers  and  looked  after  the  milk 
supply.  The  babies  were  brought  in  each  week  and  esc  ami  ned  and  weighed  by 
medical  men. 

The  spheresof  influence  of  these  stations  were  limited.  One  nurse 
could  not  properly  take  care  of  more  than  one  hundred  babies  and  one  station 
could  not  properly  look  after  more  than  three  hundred  babies.  The  milk 
stations  proved  an  excellent  means  of  looking  after  infant  welfare. 

Maternal  nursing  has  been  proven  to  be  superior  to  artificial  feeding. 
The  milk  station  did  not  try  to  encourage  artificial  feeding  but  rather  was 
designed  to  be  a valuable  means  of  encouraging  and  malcing  possible  maternal 
nursing. 

In  some  work  done  at  Detroit  bv  Price^  (^9^^)  i't-  was  found  that  eighteen 

percent  of  the  births  were  not  reported.  In  many  cases  it  has  been  noted 

that  themilk  man  is  unduly  blamed  for  ills  that  babies  are  heir  to.  Dr. 

2 

Thompson  in  summing  up  the  situation  malces  the  following  statement 

"The  question  of  ir^fant  mortality  is  eighty  percent  education  of  the  mothers 

and  tv/enty  percent  milk.  To  successfully  combine  milk  with  a baby,  you 

must  take  care  of  the  baby  as  well  as  the  milk." 

5 

Helmholz  end  Hoffmann  i^i  analizing  the  records  of  the  Infant 

Welfare  Stations  of  Chicago  in  19^5  found  that  ninety-three  percent  of  the 


•■ ' ■'  \ ’.f-  ■ 1^'^, 

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.>:  'J.Jm^::m:.^^i^Hi. V::&  JfLL}m:^ . 


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i.  ;’.-4'  '.  • 4>-  ' :,/  * .*  - ' ■ . ■ •■■■■'  > » >'iyys  ikiklv^A. 

-A'::  i^'|:»'.’*  ^ ■ V-'-.  ? 'vJi^,  ^ '77-  ,,  {Ji® 

rf  '^>1.  .;V’'‘^  ;’  ik.  . . *.  -3.  "V  * » “Lt » JP  •_  . . . •ii.'i.  w7 '.>  rw,..  /. -i  A 


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21 


deaths  were  in  families  with  an  income  of  fifteen  dollars  or  less  per  week. 
They  found  that  about  sixty  percent  of  the  deaths  from  the  sammer  gastro- 
intestinal disturbances  were  in  children  who  were  admitted  to  the  stations 
during  July,  August  and  September. 

Diarrheal  Diseases. 

Diarrhea  seems  to  be  quite  a common  and  prevalent  disease  among  infante. 
The  disease  seems  to  get  a better  foothold  in  the  siumner  during  the  hottest 
months.  It  has  been  noted  that  along  with  a high  bacterial  count  in  milk 
that  diarrhea’s  were  more  common. 

Children  who  are  not  up  to  physical  standard  or  are  congenitally 
weak  are  very  susceptible.  It  has  been  especially  noted  that  babies  from 
two  to  xour  months  of  age  especially  those  that  have  been  recently  weaned 
seem  to  be  the  most  susceptible  to  the  disease.  The  humidity  has  been 
founa  to  be  a big  factor  in  the  diarrheas..  Carbohydrate  fermentation  was 
fo'und  to  play  an  important  part  in  many  of  the  diarrheas.  A formula  low 
in  sugar  is  recommended  for  treatment. 

Hill  (lolo)  in  a study  of  diarrheas,  of  infants  gives  three  types  of 
diarrhea;  mechanical  diarrhea,  due  to  mechanical  irritation,  fermentative 
diarrhea,  due  to  chemical  irritation  and  infectious  diarrhea,  due  to  bac- 
terial infection.  The  mechanical  diarrhea  was  found  to  be  most  common  in 
children  over  one  year  of  age.  Paw  fruits  often  cause  it.  The  fermentative 
diarrhea  was  found  to  be  m®re  co.mmon  to  children  under  one  year  of  age. 

It  was  said  to  be  caused  from  the  following;-  too  high  sugar  content 
in  feed,  parental  infections,  overheating,  nervous  exhaustion  and  excite- 
ment and  constitutional  weaknesses. 


22 


Bibliography 

1 Taylor,  ?.E.  and  Van  Ingen,  ?.  M.D.;  Infant  Mortality  and  Milk  Stations. 

New  York  Milk  Committee  (19^2). 

2 Price,  Win.  H.  M.C.;  Some  Statistics  Regarding  Infant  Mortality,  ^rd 

Annual  Report  of  the  International  Assoc,  of  Dairy  Milk 
Inspectors,  pp.  95- 

J Helraholz,  H.F.  and  Hoffmann,  W.  M.D.j  An  Analysis  of  the  Mortality  for 

19^5  in  the  Infant  Welfare  Stations  of  Chicago.  Am.  Medical 
Journal  (19^6)  :6j  p'^rt  2 pp. 

A Hill,  Lewis  Webb  M.D.j  The  Etiology  and  Treatment  of  Diarrheal  Diseases 
of  Infants.  Journal  Am.  Med.  Assoc.  72:16^^,  (^9^9)* 

Conn,  H.W.j  Diarrheal  Diseases.  Practical  Dairy  Bacteriology.  Orange 
Judd  Co.  C 1910). 

Grover,  J.I.  M.D.j  A Study  of  the  Diarrheas  in  Boston  for  19^5*  Am.  Med. 

Assoc.  Journal  Vol.;67  part  2 pp.  1^62-1^67  (l9^o)* 


25 


V.  Lectio  Acid  Becteria. 

The  curdling  and  souring  of  milk  is  a phenomona  which  hes  been  known 
for  ages  but  not  until  within  comparatively  recent  years  has  the  cause 
for  this  been  understood, 

Esten^(l69^)  isolated  forty  seven  organisms  from  milk.  He  thought 
them  all  to  be  identical.  He  examined  milk  from  thirty  widely  separated 
localities  and  found  with  t\vo  exceptions  the  same  organism  to  be  present. 
This  fact  led  him  to  believe  that  one  organism  universally  existed,  in  the 
territory  he  studied  which  caused  the  ordinary  curdling  and  souring  of 
milk.  The  organism  isolated  he  found  to  be  identical  with  the  organism 
isolated  by  Gunther  and  Thierfielder  who  concluded  that  their  organism 
was  the  same  as  Lister's  Bacterium  lactis  and  Hueppe's  Bacillus  acidi 
lactici . 

Conn  and  Esten~( I90A)  found  the  following  phases  to  be  present  in 
milk:- 

Lag  phase  or  period  at  the  beginning  where  there  is  no  increase  in 
bacteria.  In  this  phase  some  species  meeting  with  an  unfavorable  environ- 
ment die  aut.  The  length  of  such  a period  depending  upon  the  temperature. 
After  the  preliminary  period,  c period  or  phase  of  rapid  multiplication 
of  bacteria  in  the  milk  then  follows.  The  temperature  seems  to  govern  the 
types  that  develop.  In  the  next  phase  other  forms  of  bacteria  other  than  Sihe 
lactic  acid  flora  seem  to  be  killed  out.  This  is  probably  due  to  the 
acid.  About  ^0  per  cent  of  the  flore  then  present  is  made  up  of  the  lactic 
acid  type.  The  aerogenee  type  of  lactic  acid  bacteria  which  are  the  gas 
producers  seem  to  be  favored  by  a temperature  of  57  degrees  centigrade. 

The  aerogenes  type  is  an  enemy  to  the  butter  end  cheese  maker. 


2h 


The  curdling  point  of  milk  was  found  to  be  independent  of  the  number 
of  bacteria  present.  Milk  was  found  to  curdle  under  different  donditions 
when  having  a bacterial  count  as  low  as  8,000,000  per  C.C.  On  the  other  hand 
a count  as  high  as  4,000,000,000  bacterir  per  C.C.  has  been  obtained  before 
milk  would  curdle.  Various  reasons  which  are  still  unsettled  have  been 
given  to  explain  this  phenomona. 

A great  deal  of  confusion  arose  in  the  past  in  regard  to  the  morphology 
of  the  lactic  acid  organism.  It  was  known  by  a good  many  of  the  early 
investigators  as  Bact.  lactis  acidi.  Kruse'Cent.  f.  Bac.  u.  Par. I. , XXXIV, 
P757f  1905)  J'nd  Heinemann  (Cent.  f.  Bac.  u Par.  II.,  XVI,  p.558,  I9O6) 
insisted  that  there  was  no  such  a thing  as  Bact.  lactis  acidi  and  that  all 
of  the  organisms  which  had  been  so  named  were  cocci  which  should  be  called 
Streptococcus  lacticus.  Conn  and  Esten^( I9O6)  preferred  classifying  the 
organisms  separately. 

Esten'^^(  I9O9)  isolated  the  Strep,  lacticus  from  corn  plants  and  quite 
frequently  from  the  mouths  of  cattle.  He  concluded  that  the  cow’s  mouth 
was  evidently  the  most  abundant  source  of  the  organism  so  far  as  cow’s 
milk  was  concerned. 

The  lactic  acid  organism  is  a very  beneficial  organism  as  far  as  man 
and  milk  are  concerned.  It  is  very  important  in  giving  the  proper  flavoring 
to  butter  and  cheese.  It  also  is  of  importance  in  that  it  inhibits  types 
of  bacteria  which  are  pathogenic  or  otherwise  undesirable  from  gaining 
much  headway  in  milk.  It  is  an  organism  that  is  apparently  not  pathogenic 
for  man.  According  to  Metchnikof f ’ s theory,  which  was  later  proven  untrue, 
it  is  beneficial  when  in  the  intestinal  tract  of  man  as  it  inhibits  other 
undesirable  forme  from  developing. 


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25 


Bibliography 

1 Eaten,  Bacteria  in  the  Dairy.  XII  Bacillus  Acidi  Lactici  and 

other  Acid  Organiaraa  Found  In  American  Dairies.  9th  Annual 
Rpt.  of  the  Storrs  Agr.  Exp.  Sta.  ( I896) 

2 Conn,H.^.  and  Eaten,  ; The  Effect  of  Different  Temperatures  in 

Determining  the  Species  of  Bacteria  which  Grow  in  Milk. 
Storrs  Agr.  Exp.  Sta.  I6th  Annual  Rpt. 

p Conn,  H.W.  and  Esten,  ^.M. ; Classif icration  of  Dairy  Bacteria.  Strept. 

lacticus.  Storrs  Agr.  Exp.  Sta.  Rpt.  for  I9O0  pp.  9^-205 

E. s.R.  vol.ie  p.  979. 

A Esten,  '17. M. ; Bacterium  Lactis  Acidi  end  Its  Sources.  Storrs  Agr.  Exp. 
Sta.  Bui.  No.  59  ^9^9 

Rogers,  Lore  A.  and  Davis,  Brooke  J. ; Methods  of  Classifying  the  Lactic- 
Acid  Bacteria.  U.S.  Dept,  of  Agr.  Bureau  of  An.  Industry 
Bui.  15^1  f 1912) 


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26 


VI  Milk  PaeteurizBtion. 

Pasteurization  is  now  known  universally.  Much  has  been  written  and  a 
great  deal  of  woric  has  been  done  on  this  subject.  Pasteur  (1879)  was  one 
of  the  early  workers  in  this  field.  A great  deal  of  hie  work  was  done  on 
liquors.  The  following  statement  was  made  by  Pasteur V 1679) "Our  proposition 
concerning  the  causes  of  the  disease  of  wort  and  beer  might  be  demonstrated 
in  several  ways.  The  following  is  the  simplest;-  "Take  a few  bottles  of 

sound  beer Place  some  of  these  bottles  in  a hot  water  bath  and  raise 

the  temperature  to  about  60  degrees  centigrade  ( 140  degrees  P.).  Permit 
them  to  cool  and  then  place  them  by  the  side  of  the  other  bottles  that  have 
not  been  heated.  In  every  case  especially  if  we  conduct  this  experiment 
in  the  summer,  we  shall  find  in  a few  weeks,  the  length  of  time  varying 
with  the  temperature  and  quality  of  the  beer,  all  bottles  which  have  not 
been  heated  have  become  diseased,  in  some  cases  even  to  the  extent  of 
becoming  undrinkable ." 

The  term  "pasteurization"  was  first  used  in  recognition  of  Pasteur's 
discoveries  on  the  causes  of  the  deterioration  of  fennented  liquors  and 
the  means  of  preserving  such  liquors  by  the  application  of  heat.  Later  the 
term  was  given  wider  significance  and  applied  to  milk. 

Koplik^( I89I ) made  the  following  statement:-  "As  intimated  it  would 
be  ideal  to  sterilize  milk  in  small  or  large  quantities  at  the  dairies, 
but  this  has  never  yet  been  attempted  in  this  city."  Pasteurization  today 
is  now  used  in  most  of  the  larger  cities  in  this  country. 

The  temperatures  first  used  in  the  pasteurization  of  milk  were  around 
155  degrees  P,  for  a period  of  15-20  minutes.  Heating  milk  above  1^0  degrees 
P.  was  fo'ond  to  change  the  physical  conditions  of  the  fat  globules  and  the 


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27 


cream  loses  its  property  of  rapid  creaming.  A temperature  of  1^0  degrees  F. 
was  found  to  kill  out  the  vegetative  forms  in  20  minutes. 

The  proper  amount  of  heating  has  been  determined  in  many  cases  from 
the  resistance  or  thermal  death  point  of  tubercle  bacilli.  A temperature 
and  time  sufficient  to  kill  out  tubercle  bacilli  is  much  desired.  A temperature 
of  60  degrees  centigrade  (1^0  degrees  F.)  for  15-20  minutes  was  found 
to  kill  tubercle  bacilli  when  they  were  suspended  in  distilled  water, 
physiological  salt  solution,  bouillon  and  milk.  The  tubercle  bacilli  in 
the  pellicle  of  milk  which  foms  upon  sterilization  were  found  to  live  at 
least  as  long  as  60  minutes  at  60  degrees  centigrade.  In  later  types  of 
pasteurizers,  pellicle  growth  did  not  form  as  the  milk  was  heated  in 
closed  containers.  Preventing  the  formation  of  the  pellicle  in  the  milk 
upon  heating  thus  was  a great  stride  in  making  pasteurization  more  effect- 
ive. 

The  effect  of  higher  temperature  exposures  for  a shorter  period  of 
time  was  tried . (Closed  containers  being  used).  Heating  to  a temperature 
of  160  degrees  F.  for  a period  of  one  minute  was  found  sufficient  to 
destroy  the  virulence  of  bovine  tubercle  cultures  so  that  the  disease 
was  not  produced  in  experimental  animals,  such  as  guinea  pigs  when  inoculated 
with  cultures  ranging  from  2-5  mgrs. 

Rogers^( I905)  found  that  milk  held  at  10  degrees  centigrade  was  in 
good  condition  from  a bacteriological  standpoint  48  hours  after  pasteur- 
ization. The  same  milk  held  at  20  degrees  centigrade  for  24  hours  he  considered 
not  a safe  food.  He  found  a large  number  of  peptonizing  bacteria  developing 
in  pasteurized  milk.  The  same  phenomena  was  observed  in  raw  milk  and 
especially  in  raw  milk  held  at  lower  temperatures.  In  raw  milk  kept  at 


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26 


room  temperatures  the  acid  developing  from  the  lactic  acid  bacteria 
probably  check  the  peptonizing  flora  and  keep  it  from  developing. 

Reinfection  of  pasteurized  milk  may  readily  occur  and  the  infecting 
organisms  may  gain  more  of  a foothold  than  they  could  in  raw  milk. 

Attention  has  been  called  to  this  by  some  authors  and  a few  cases  have 
been  brought  up  to  substantiate  such  a.  belief. 

In  later  work  the  above  statements  have  been  objected  to.  Ayers 
and  Johnson‘^’(  I9IO)  find  that  commercially  pasteurized  milk  alv/ays  sours 
because  of  the  development  of  lactic  acid  bacteria,  which  on  account  of 
their  hig}i  thermal  death  point  survive  pasteurization.  They  find  that  and 
old  taste  developing  in  the  milk  is  not  characteristic  of  pasteurized  milk. 
They  find  the  relative  proportion  of  the  groups  of  peptonizing,  lactic 
acid,  andalkali  or  inert  bacteria  ie  approximately  the  same  in  efficiently 
pasteurized  milk  as  it  is  in  clean  raw  milk. 

The  "holder"  process  has  been  compared  to  the  "flash"  process  in 
the  pasteurization  of  milk.  From  work  viiich  has  been  done  so  far  the 
holder  precess  is  considered  by  many  investigators  to  be  the  best. 

However  there  is  another  aspect  to  the  problem  and  that  is  the  matter  of 
time  and  expense.  In  the  matter  of  chemical  changes,  milk  pasteurized 
by  the  holder  process  62.6  degrees  centigra.de  (1^5°  F)  for  thirty  minutes 
was  found  to  undergo  no  appreciable  change.  As  the  temperature  increases 
the  amount  of  coagulated  albumin  increases. 

Electrical  pasteurizers  have  teen  devised  v/hich  seem  to  work  very 
effectively  in  killing  out  tubercle  bacilli  and  otlier  undesirable  organ- 
isms. The  disease  producing  organisms  are  likewise  killed  out.  I^ilk 
has  been  fo'und  to  keep  three  or  four  days  by  such  a treatment.  The  chem- 


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29 


ical  constitution  of  it  was  found  to  vary  little. 

A biorisator  process  of  pasteurizing  milk  has  also  been  worked  out. 

By  this  process  of  heating  no  albumin  coagulum  results  and  the  fat  globules 
are  the  same  as  in  raw  milk.  Vegetative  bacterial  forms  and  pathogenic 
germs  are  ell  destroyed  by  the  biorisator. 

A study  of  the  germicidal  action  of  the  ultra-violet  rays  has  been 
made.  The  ultra-violet  rays  produced  by  the  Cooper-Hewitt  mercury  ai’c 
have  a strong  bactericidal  action.  This  means  of  rendering  milk  safe 
for  drinking  purposes  may,  however,  have  some  practical  significance. 

Much  improvement  in  regard  to  the  organization  and  the  control  of 
pasteurization  needs  be  made.  It  is  very  easy  for  a man  of  little  or  no 
experience  or  training  along  bacteriological  lines  to  modify  pasteuriza- 
tion in  such  a way  as  to  lose  all  of  the  beneficial  results  or  effects 
which  should  be  derived  from  it.  The  two  big  factors  to  keep  in  mind 
are  the  proper  time  and  temperature.  Often  the  proper  amount  of  attention 
is  not  given  to  these  facts. 

Tonney5( 1^20)  suggested  that  a ”shut-off”  system  be  used  in  enforcing 
certain  important  measures  in  the  pasteurization  and  handling  of  milk.  By 
"shut-off"  is  meant  a temporary  suspension  of  permit  to  operate  a pasteurizing 
plant.  For  the  following  reasons  it  is  resorted 

1.  "Non-compliance  with  orders  for  abatement  of  inssnitaiy  conditions. 

2.  Acceptance  of  milk  from  other  shippers  who  have  attempted  to  evade 
a "shut-off". 

5*  Failure  to  send  thermo  recorder  cherts  to  the  department. 

4.  Falsifying  thermo  recorder  charts. 

5*  Failure  in  cose  of  a new  plant  to  apply  for  a permit  before  ship- 


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50 


ment . 

6.  High  terapereture  of  milk  at  the  receiving  platform  in  the  city. 

7-  Excessive  bacterial  content  of  the  milk  sampled  at  the  receiving 
platform. " 

Not  until  some  measures  toward  enforcement  are  taken  can  we  expect 
to  obtain  milk  which  has  been  properly  pasteurized  and  cared  for. 

Pasteurization  is  a very  safe  and  sane  process.  7?hen  it  is  properly 
carried  out  much  disease  due  to  milk  will  be  eliminated.  Pasteurization 
of  milk  does  not  free  it  from  reinfection  such  as  some  people  seem  to 
think  it  does.  Care  should  be  taken  of  it  to  keep  it  in  clean  places 
and  well  refrigerated.  Pasteurization  v^en  properly  carried  out  can  eliminate 
disease  due  to  milk  and  insure  the  safety  of  its  users. 


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